Improvement effects of knee-bracing friction dampers on cyclic behavior of steel joints in antique buildings

Abstract

To inherit the unique characteristics of historical timber architecture, the steel antique building (SAB) imitating ancient Chinese timber structures has been constructed using contemporary steel materials and fabrication techniques. These buildings typically exhibit premature yielding cracks and weak energy dissipation at the beam ends under seismic loads. To improve the seismic performance of SABs, two different types of friction dampers were deployed at the knee-bracing region around beam-column joints in SABs. First, cyclic loading tests on dampers indicate that both shear friction dampers and rotational friction dampers exhibit full hysteretic behavior, demonstrating an excellent and stable energy dissipation capacity. The friction coefficient of dampers with brass pads was theoretically calculated to be 0.35. Second, the quasi-static test showed that failure of steel joint specimens with knee-bracing dampers primarily occurred at replaceable angles in the beam-column connection region, which demonstrates that the repairability of steel joints in SABs can be greatly improved without overcomplicated labor. Adding knee-bracing dampers effectively postpones damage to the replaceable angles, which improves the strength, stiffness, and energy dissipation capacity of the steel joints significantly. The shear damper exhibits a more pronounced improvement in the overall structural seismic performance compared to the rotational damper with the same frictional sliding force. Moreover, numerical simulations showed that the strength of the proposed joints with knee-bracing friction dampers decreases with an increase in the axial compression ratio, while increasing the thickness of angles or the sliding force of dampers can effectively improve the seismic performance of the steel joints in SABs.